The present invention relates generally to the control of liquid temperature in a liquid bath so that the temperature is uniform throughout the bath, and more particularly, to a method of and a system for controlling the heating of the bath liquid so that a desired constant liquid temperature is maintained throughout the bath notwithstanding the transport of objects to be heated by the bath through the bath liquid, or other causes of sudden changes in the ambient temperature conditions.
Liquid bath temperature control for maintaining a desired bath liquid temperature while containers of liquid samples to be heated are transported through the bath are typically embodied in automated clinical analysis systems such as disclosed in U.S. patent application Ser. No. 575,924, filed Feb. 1, 1984, and assigned to the assignee of the present invention. The contents of Ser. No. 575,924 application are incorporated in their entirety by reference in the present application.
In clinical analysis systems such as the one disclosed in Ser. No. 575,924 application, a series of cuvettes are transported in the form of a belt through a heated water bath so that, when a patient sample and a reagent are mixed in each cuvette prior to photometric analysis, the reaction mixture will be at a predetermined incubation temperature on which computations carried out by the analyzer are based.
It will therefore be understood that if the actual reaction mixture temperatures in the cuvettes are not at the assumed level of temperature; for example, 37.0 degrees Centigrade (C.), the analyzer data will be subject to error. In fact, the analyzer data can be affected as much as 8% per degree C., for such changes in sample temperature.
The prior bath temperature control arrangement basically included a heating element for heating water entering a bath tank through which the cuvette belt was transported. The water influent entered the tank through a fitting passing through the bath tank bottom plate, the fitting having a hose connected to it which laid in the bath parallel to the bottom plate. The downstream opening of the hose was directed over a water temperature sensor within the bath tank, the sensor having an unspecified time constant.
Temperature control for the bath water was carried out by turning the heating element on until the desired temperature was detected by the sensor next to the inlet hose opening. The prior temperature control could not, however, always assure that the bath water temperature was uniformly regulated to within plus or minus 0.1 degrees C. of the desired 37 degrees C. incubation temperature for the sample and reagent mixture during photometric analysis. Even after an "air sensor" was connected in series with the water sensor, calibration of the air sensor was difficult, and the overall system still would not hold the bath water temperature constant during changes in ambient temperature level. Further, a relatively long time period was required for the bath temperature to return to the desired level after parts of the analyzer in the region of the bath were removed and replaced during maintenance.